1. Field of the Invention
This invention relates to injection systems and in particular, to a fuel injection system for internal combustion engines.
2. Prior Art
Moore et al, U.S. Pat. No. 4,487,181, discloses a fuel supply system for an internal combustion engine and includes a memory associated with a fuel pump for storing fuel delivery data specific to that pump, which data has been previously ascertained during a bench test. The patent states that the memory will contain information regarding the amount of fuel pumped for different settings of the distributor member. The pump has an axially slidable rotary distributor member. Since the pump output will tend to vary with speed, the tests could be carried out at a number of different speeds. There is no specific disclosure of providing test data in the nature of pulse width correction times for a number of plungers in a spill control fuel delivery system.
Thus there is described a fuel supply system comprising a distributor type fuel injection pump, a memory containing a test record of the pump, and a control system controlling the fuel quantity and injection timing. The control system controls the fuel quantity by controlling axial position of a distributor member in the pump. It utilizes the information on the test record of the pump to assure that the desired amount of fuel is supplied to the engine. The patent does not address the issue of equal cylinder to cylinder fuel distribution. The patent states that the control system will seek to establish a particular axial position of the distributor member when a particular demand is made by an operator. In such a mode of operation, each position of the distributor member can assure only that the average fuel delivery to a multicylinder engine corresponds to the desired quantity. The quantities delivered to individual cylinders can still differ from on another.
The Moore et al patent also does not address the issue of cycle to cycle variability. For a given position of the distributor member (or another operating parameter of the pump) the fuel delivery averaged over a number of cycles can correspond to the desired quantity, while the actual delivery during a single cycle can sill vary from cycle to cycle and differ from the required value.
McHugh et al, U.S. Pat. No. 4,402,294, discloses a fuel injection system for a Plurality of electromagnetic fuel injectors having wide manufacturing tolerances, and wherein accurate fuel control is attained by adjusting the pulse width for each injector based on test data stored in a digital memory. With reference to FIGS. 1 and 2, each fuel injector 7 has associated with it a calibration resistor 12 which may represent the absolute fuel flow rate or the percent deviation of the fuel flow rate from a predetermined design valve for that particular fuel injector. In determining the proper pulse width for each fuel injector, the control system 14 samples the particular resistor and retrieves from a memory 18 the correction for that injector and then calculates the duration of the actual injection pulse.
Thus the patent describes a central fuel injection (CFI) system for an engine including a single solenoid controlled injector connected to a constant pressure common rail fuel supply system. Whenever the solenoid opens the injector outlet valve, fuel is injected through the outlet orifice. The quantity of fuel injected is determined by the product of the flow rate and the injection duration.
According to the patent, the injector is equipped with a resistor selected from a number of resistors during advance testing of the injector flow rate. The resistance of the resistor reflects the deviation of the measured flow rate from the design valve. The control system measures the resistance, interprets it in terms of percentage deviation with the aid of a table of data and makes correction in the algorithm used to compute the required pulse duration.
First, the method is applicable only to CFI or EFI systems in which the fuel flow is orifice controlled and thus the flow rate remains constant at all engine speeds. It is not usable in systems utilizing engine driven fuel injection pumps where the flow rate varies with engine speed and is affected by internal leakage which can be different for each plunger.
Second, the method does not consider the fact that the injection duration is not equal to the solenoid voltage pulse. It differs from the latter by the duration of valve opening delay and valve closure delay which may differ from injector to injector. To take this into account would require the injector to carry additional information which a single resistor cannot accommodate.
Third, since a finite number of resistors with different resistances is available, the resistance selected is, in most cases, only an approximate indication of the necessary correction. To minimize the error, very large number of resistors with resistances differing in small increments is necessary, but the error is always there. In contrast, when digital memory is used, it is always possible to enter into the memory the exact number representing the required correction.
Fourth, the table of numbers (the lookup table) contained in the memory of the system serves only for interpretation of the resistance which is measured in ohms in terms of percentage points of deviation from the design flow rate. It is the same table for all engines and is not a table of correction values providing information on individual pump characteristic.
Fifth, the issue of providing equal cylinder to cylinder fuel distribution is not addressed.
U.S. Pat. No. 4,475,507 to Miyaki et al describes a control system for controlling fuel injection quantity delivered by a single plunger distributor-type electromagnetically controlled pump. The fuel quantity is controlled by controlling the spill valve closing duration which is divided into prestroke duration Q.sub.R during which no injection takes place and injection duration Q.sub.e. Sets of Q.sub.R and Q.sub.e data are prestored in the system memory, each set corresponding to a specific engine operating condition (speed, throttle position, etc.).
In a first embodiment, the system determines engine operating conditions, reads Q.sub.e and Q.sub.R corresponding to said condition, adds them and applies a pulse of (Q.sub.R +Q.sub.e) duration to the solenoid valve. In a second embodiment, the values of Q.sub.R are modifiable during engine operation. The system maintains the idle speed of the engine within prescribed limits by making incremental changes in the Q.sub.R value in a feedback fashion whenever the idle speed deviates from the required value. A third embodiment differs from the first and the second embodiments in that there are separate Q.sub.R values for each engine cylinder, and each is feedback controlled during engine operation as a function of engine speed or other parameters. A fourth embodiment deals with setting a maximum limit for the value (Q.sub.R +Q.sub.e)=Q.sub.max.
As a result, in the Miyaki patent, the values Q.sub.R and Q.sub.e stored in the memory represent engine fuel requirements at various operating conditions. They are the same for all engines of a certain class and they do not reflect the individual pump characteristic. In other words, this is not a pump memory of the pump individual characteristic, but the engine memory of its fuel requirements. To the extent that the values Q.sub.R are modifiable, they are modified during engine operation in a feedback fashion. In column 9, lines 6-21, there is a discussion of correcting four values Q.sub.R(i), one for each engine cylinder, one after another so as to achieve uniform fuel delivery to all cylinders even if there is a variation in nozzles characteristics. It is not clear what would assure uniform fuel delivery. The subsequent lines 22-38 appear to confirm the impression that what is described is a feedback system in which the values Q.sub.R are corrected during engine operation.
U.S. Pat. No. 4,494,507 to Yasuhara describes a control system to control the rate of fuel injection in a feedback manner on the basis of a feedback signal provided by a sensor which measures the lift (displacement) of a valve through which the fuel is pumped.
U.S. Pat. No. 4,495,915 to Shinoda et al describes a solenoid controlled electromagnetic fuel injection pump and a control system. The control system determines the required fuel delivery and timing as a function of throttle position, engine speed, etc. and computes the required duration of injection. The injection begins some time after solenoid activation. The patent teaches a pressure sensor which senses the pressure in the plunger chamber in the Pump and signals to the control system the timing of the beginning of injection. The control system starts counting the time from this moment. There is nothing in the patent that would assure that the actual fuel delivery will equal the required amount. The issue of cylinder to cylinder fuel distribution is not addressed.
U.S. Pat. No. 3,575,145 to Steiger describes a fuel injection system in which the fuel delivery to all cylinders of an engine is equalized by making adjustments in individual fuel deliveries during engine operation on the basis of continuous measurements of the deliveries in individual injection lines. This is a feedback system. It does not involve a memory storing information on the individual pump characteristic.
U.S. Pat. No. 3,587,547 to Hussey et al describes a particular high pressure common rail fuel injection system. It does not address the problem of equal cylinder to cylinder fuel distribution.
U.S. Pat. No. 3,835,819 to Anderson includes a detailed description of a fuel delivery and spark ignition control system. The main feature of the system is the use of digital electronics rather than analog circuits which were in wide use at that time. The system includes a digital data memory containing data on engine fuel requirements at various operating conditions. The memory contains no information on the individual injectors characteristics, and the question of cylinder to cylinder fuel distribution is not addressed.
U.S. Pat. No. 4,248,194 to Drutchas et al describes a control system to control flow from a pump by changing the speed of a motor driving the pump according the changing operating conditions. A digital embodiment of the invention includes a memory containing data on the pump characteristic. However, the above data are obtained statistically by testing a substantial number of pumps. No information on individual pump characteristics is provided, and the problem of equal cylinder to cylinder fuel distribution is not addressed.
U.S. Pat. No. 4,366,541 to Mouri et al describes a system controlling ignition timing and fuel flow in an engine equipped with a single central injector. The fuel flow is controlled by varying the injector valve opening duration as a function of air flow, RPM, temperature, etc., which are measured by sensors during the engine operation. The system includes a memory containing correction values to compensate for inaccuracy of measurements performed by the air flow sensor and/or other sensors. The correction values are entered into the memory at the time of motor vehicle delivery or at subsequent inspections and eliminate the need for mechanical adjustment. This patent teaches matching a fuel system to an individual engine and its sensors and does not relate to a fuel injection system which can be installed on any engine and deliver the same quantity of fuel to all cylinders. The problem of equal cylinder to cylinder fuel distribution is not addressed.
U.S. Pat. No. 4,368,705 to Stevenson et al describes an engine control system controlling injection timing and maximum allowable fuel delivery in a diesel engine. As far as the fuel control is concerned, the system controls the fuel rack limit for different engine speeds and injection timings according to information contained in the microprocessor memory. The system does not control fuel delivery. Fuel flow is controlled by the engine operator and the function of the system is to prevent the operator from increasing the fuel delivery beyond a maximum limit which may be different for different operating conditions. The above invention does not address the problem of individual pump characteristics, nor does it address the question of cylinder to cylinder fuel distribution.
U.S. Pat. No. 4,398,515 to Canup et al describes a diesel engine control system which controls fuel delivery as a function of engine speed by controlling a metering valve of a fuel injection pump in accordance with data contained in a microprocessor memory. There is nothing in the system that would assure that a given position of the metering valve stop will actually produce the required fuel delivery with required precision. The invention does not address the problem of individual pump characteristic. The question of equal cylinder to cylinder fuel distribution is not addressed either.